How to transform text to multiselect?

I have a text field which I would need to transform into multiselect. Delimiter is comma.
Here is example:

Currently only viable option for me is to do it manually. Or am I missing something that would solve my problem?

Is this transformation something that you need to done just once, or occasionally, or does it need to happen automatically whenever the source data changes?

Would you be updating an existing multiselect field (adding to its existing options), or overwriting it, or creating a new multiselect field?

Hi, Matt! I would need to be done when a record is updated, so automatically. I would need to update existing multiselect field with another option.

Actually, I might find a solution for this. Instead of using multiselect field I can use relation many-to-many and therefore adding new options automatically is not going to be a problem.